Oil and gas drilling rigs are located throughout the world, both on land and at sea. There are important differences between the types of drilling rigs used for inland sites compared to those used for offshore drilling. An offshore drilling rig is typically very large, and may be made as a unitary structure. The electrical power generation and distribution system can be built on an offshore rig before the rig is moved into its operating location. This allows for hardwired connections and other permanent or semi-permanent electrical connections in the electrical distribution system.
Many inland oil and gas drilling rigs are much smaller than their offshore counterparts. It is common for inland rigs to be constructed in a more modular form, with the various parts of the rig being put together at the drilling location. A rig of this type may be hauled to the drilling site on one or more trucks. Because the rig is delivered in parts and assembled on site, the electrical distribution system is often prepared on site, as well. It is not common to have an electrical power distribution system pre-wired for a smaller inland drilling rig.
The field assembly and installation of many inland drilling rigs has led to widespread use of single pole electrical connectors that can be prepared in the field. A pin and collet style single pole connector has been used on inland oil and gas drilling platforms for many years. A typical connector of this type has a threaded shaft at one end and a threaded collet at the other end. This type of connector is shown in FIG. 6. One power line, typically the input line, is connected to the threaded shaft end of the connector. A pin is connected to the end of the other electrical cable, typically the output line, and this pin is placed inside the collet. A large collet nut is then tightened to create a secure connection. Some type of insulating boot or cover is then positioned over the collet and pin portion of the connection. Another boot or cover may be used to cover the threaded shaft connection, as well.
These single pole connectors are mounted in a distribution panel. The panels are typically made of melamine, fiberglass, or some other electrically nonconductive material. Holes are drilled into the panels, and the connectors are pressed into the holes. The panel connection portion of the single pole connector is typically knurled or grooved to create a more secure fit with the distribution panel. This fit is important to the operation and use of the connectors in this harsh environment.
The connectors are usually mounted into the distribution panels before the connection is made. This method of completing the electrical connection with a pin and collet type connector results in a great deal of torque applied to the connection between the connector and the distribution panel. When an oilfield worker tightens the large collet nut, the entire connector will tend to rotate. Such rotation is prevented only by the connection between the connector and the distribution panel. Because this connection to the panel is not very strong or secure, it is common to have the connector strip its connection to the distribution panel, and thus turn freely within the mounting hole in the panel. When this happens, it may be very difficult to make or unmake the pin and collet connection. In addition, when the connector strips its connection to the distribution panel, another hole in the panel must be drilled, and the connector reinstalled or a new connector installed. These failures and the necessary follow-up actions add time and cost to the overall operation.
Improvements have been made to single pole connectors to address the problem of a connector striping its connection to a distribution panel. The most common improvement is the machining of splines into the body of the connector. These splines engage the distribution panel when a connector is pressed into a hole in the panel. The splines, however, are not enough to prevent many connectors from stripping in distribution panels. Despite this problem, splined connectors of this type have been widely used in the oilfield for many years.
Another improvement consists of a set screw or key in the connector that engages a slot cut into the edge of the mounting hole in the distribution panel. This configuration creates more resistance to the torque applied when the collet nut is tightened, but it also requires additional installation time. A slot must be cut into the panel after the normal mounting hole has been drilled out. Even when this system is used, some of the connections to distribution panels will strip out.
The standard pin and collet configuration also results in a less than optimal connection. The collet nut must be tightened a great deal to provide a mechanically secure connection. If a pulling force is applied to the cable with the pin on its end, the pin may pull out of the collet, thus causing arcing and a loss of electrical connection. The arcing may create a fire risk or a direct risk to nearby personnel. To reduce the risk of pull out, workers tend to tighten the collet nuts as tight as possible. To do this, workers apply a great deal of torque to the collet nuts, which, in turn, causes more of the connectors to strip out the connections to the distribution panel. One shortcoming of this arrangement (i.e., the possibility of pin pull out) thus exacerbates another shortcoming (i.e., the stripping of the panel connection).
The threaded shaft end of these common single pole connectors also poses problems in use. A bus bar type connection is generally preferred for making a reliable, low-resistance connection. A standard lug connection may be crimped onto the end of an electrical cable, and the lug connected to the bus bar using a standard bolt and nut connection. It would be a further improvement on the common design to include a bus bar type connection on the end opposite the collet.